The P2X7 receptor (P2X7R) is an ATP-gated ion channel expressed by monocytes and macrophages. This study generated P2X7R-deficient mice to investigate the receptor's role in interleukin (IL)-1β post-translational processing. P2X7R-deficient macrophages responded to lipopolysaccharide (LPS) and produced levels of cyclooxygenase-2 (COX-2) and pro-IL-1β comparable to wild-type cells. However, in response to ATP, pro-IL-1β produced by P2X7R-deficient cells was not externalized or activated by caspase-1. Nigericin, an alternate secretion stimulus, promoted release of 17-kDa IL-1β from P2X7R-deficient macrophages. In vivo, both wild-type and P2X7R-deficient animals showed increased peritoneal lavage IL-6 levels after LPS injection but no detectable IL-1. Subsequent ATP injection to wild-type animals increased IL-1, leading to additional IL-6 production, while ATP-treated, LPS-primed P2X7R-deficient animals did not show similar increases. The absence of P2X7R prevented peritoneal macrophages from releasing IL-1 in response to ATP, impairing cytokine signaling cascades. These results demonstrate that P2X7R activation can provide a signal for IL-1β maturation and release, initiating a cytokine cascade. IL-1 is a multipotential inflammatory mediator produced by activated monocytes and macrophages. When released, IL-1 binds to receptors on target cells, initiating signaling cascades that up-regulate gene products contributing to inflammation, including matrix metalloproteinases, COX-2, IL-6, and cellular adhesion molecules. Two forms of IL-1, IL-1α and IL-1β, contribute to IL-1 biological activity. Both pro-IL-1α and pro-IL-1β are synthesized without a signal sequence, leading to their accumulation in the cytoplasmic compartment of producing cells. Caspase-1 is also produced as a cytosol-localized proenzyme, which must be proteolytically processed to generate the mature active protease. In activated monocytes and macrophages, pro-IL-1β and procaspase-1 co-exist within the cytoplasm. Mechanisms controlling procaspase-1 activation and pro-IL-1β cleavage are not well understood. Recent studies suggest that post-translational processing of pro-IL-1 requires an external stimulus, such as ATP, nigericin, cytolytic T-cells, bacterial toxins, and hypotonic stress. This requirement for a secretion stimulus is notThe P2X7 receptor (P2X7R) is an ATP-gated ion channel expressed by monocytes and macrophages. This study generated P2X7R-deficient mice to investigate the receptor's role in interleukin (IL)-1β post-translational processing. P2X7R-deficient macrophages responded to lipopolysaccharide (LPS) and produced levels of cyclooxygenase-2 (COX-2) and pro-IL-1β comparable to wild-type cells. However, in response to ATP, pro-IL-1β produced by P2X7R-deficient cells was not externalized or activated by caspase-1. Nigericin, an alternate secretion stimulus, promoted release of 17-kDa IL-1β from P2X7R-deficient macrophages. In vivo, both wild-type and P2X7R-deficient animals showed increased peritoneal lavage IL-6 levels after LPS injection but no detectable IL-1. Subsequent ATP injection to wild-type animals increased IL-1, leading to additional IL-6 production, while ATP-treated, LPS-primed P2X7R-deficient animals did not show similar increases. The absence of P2X7R prevented peritoneal macrophages from releasing IL-1 in response to ATP, impairing cytokine signaling cascades. These results demonstrate that P2X7R activation can provide a signal for IL-1β maturation and release, initiating a cytokine cascade. IL-1 is a multipotential inflammatory mediator produced by activated monocytes and macrophages. When released, IL-1 binds to receptors on target cells, initiating signaling cascades that up-regulate gene products contributing to inflammation, including matrix metalloproteinases, COX-2, IL-6, and cellular adhesion molecules. Two forms of IL-1, IL-1α and IL-1β, contribute to IL-1 biological activity. Both pro-IL-1α and pro-IL-1β are synthesized without a signal sequence, leading to their accumulation in the cytoplasmic compartment of producing cells. Caspase-1 is also produced as a cytosol-localized proenzyme, which must be proteolytically processed to generate the mature active protease. In activated monocytes and macrophages, pro-IL-1β and procaspase-1 co-exist within the cytoplasm. Mechanisms controlling procaspase-1 activation and pro-IL-1β cleavage are not well understood. Recent studies suggest that post-translational processing of pro-IL-1 requires an external stimulus, such as ATP, nigericin, cytolytic T-cells, bacterial toxins, and hypotonic stress. This requirement for a secretion stimulus is not